Disposable sampler

ABSTRACT

A sampling device for removing particulate matter from a gaseous medium by jet impaction including a base, a lower impaction stage carried by the base and an upper impaction stage carried by the lower impaction stage. An apertured plate is provided in each of the impaction stages for generating a prescribed velocity of the gaseous medium as it passes therethrough, and a collection member is positioned under each of the apertured plates against which the gaseous medium impinges to collect the particulate matter thereon. Frangible locking means connect the base and stages together so that they cannot be separated without destruction of the locking means to prevent reuse. Flow regulating means is provided in the base to regulate the flow rate of the gaseous medium through the device.

United States Patent 1191 v 111 3,922,905

Roth 1451 Dec. 2, 1975 l l DISPOSABLE SAMPLER Primary Examiner- 8. Clement Swisher [76] Inventor: Thomas P. Roth, 5025 11111511010 Powell Road, Apt. 9E, Nashville, Tenn. 32715 [57] ABSTRACT A sampling device for removing particulate matter [22] Flled' May 1974 from a gaseous medium by jet impaction including a [21] Appl. No.: 469,325 base, a lower impaction stage carried by the'base and an upper impaction stage carried by the lower impac- 52 11.5. C1. 73/28 StageIAn aperfured Plate l each the impactlon stages for generatmg a prescnbed veloc- [51] Int. Cl G01N /04; G01N /02 I 1ty of the gaseous med1um as it passes therethrough, [58] held of Search 73/432 PS, 421.5, 28;

206/807 and a collection member is pos1t1oned under each of I the apertured plates against which the gaseous medium impinges to collect the particulate matter [56] References Clted thereon. Frangible locking mearis'connect the base UNITED STATES PATENTS and stages together so that they cannot be separated 985,850 3/l9ll Smith 206/807 without destruction of the locking means to prevent 2,119,283 8/1933 Raymond 73/28 reuse. Flow regulating means is provided in the base to regulate 'the flow rate of the gaseous medium I at h th 3,715,911 2/1973 Chuah 73/28 throug e devlce 12 Claims, 14 Drawing Figures l 5O l5 d1 1 1 ."I 1 e "L" r i l l 6/ /2 l l as Ill US. Patent Dec. 2, 19 75 Sheet40f4 3,922,905

DISPOSABLE SAMPLER BACKGROUND or H INVENTION Air sampling devices which use the principle of jet impaction to separate air-borne particles into classes are available on the market today such as those shown by U.S. Pat. Nos. 3,001,914 and 3,693,457. Such devices have had several stages which were serially arranged and in which the velocity of the gaseous medium being sampled as it impinges against the collecting medium is increased through successive stages. One of the primary problems with these prior art air sampling devices is that they have been extremely costly in the manufacture thereof in order to produce the required precision tolerances required for successful operation. Further, difficulty has been encountered in the regulation of the flow rate of the gaseous medium through the sampler since the classification of the airborne particles is dependent upon the velocity of the gaseous medium passing through the sampler.

As a result of the initial cost of manufacturing the prior art samplers, it was necessary for the ultimate user to reuse the sampler many times to reduce the total operating cost thereof to a reasonable figure. This has required that the sampling device itself be sterilized between each sampling operation so as to reduce contamination on the sampling device from a previous air sampling operation which could give a false reading on a subsequent operation. Moreover, most of these prior art air sampling devices have been complicated in construction thereby requiring personnel time by the ultimate consumer in assembling and disassembling these samplers before and after use. Further, considerable care must be taken in the sterilization process to ensure that the air sampler is free of contaminants for subsequent air sampling operations. Also, many of these prior art sampling devices have been hard to calibrate and to obtain consistent distribution of the gaseous medium flow therethrough.

The prior art sampling devices have also used several stages which classified the air-borne particles into a like number of classes. In most instances, however, the information desired is whether the particles are sufficiently small to be inhaled and if sufficiently small to be inhaled, whether there is lung penetration. The attempts to classify the particles as taught by the prior art into several classes has resulted in partial commingling of the classes so that the resulting readings were confusing.

SUMMARY or THE INVENTION These and other problems and disadvantages associated with the prior art are overcome by the invention disclosed herein by the provision of a simplified, inexpensive sampler construction which reduces the initial capital cost thereof sufficiently to allow the sampler to be disposable and not be reused. Further, the simplified construction of the sampler of the invention is such that it can be quickly and easily assembled by unskilled personnel without affecting the sampling capability of the sampling device. Further, the stages of the sampler are locked together by a frangible locking means so that the locking means is destroyed as an incidence of the disassembly of the sampling device't'o prevent its reuse in a contaminated condition. This destruction of the locking means further provides a ready indication that the sampling device has been used to prevent the reassembly thereof in a contaminated state. Further, a built-in air flow control device is provided which ensures essentially constant flow rates over a wide range of vacuums drawn on the device to ensure correct velocity of the gaseous medium through the sampling device and the properclassification of air-borne particles therein. Further, the sampling device of the invention incorporates a minimum number of stages to facilitate the assembly and disassembly of the device as well as requiring the minimum amount of time to check the particles separated by the device.

The invention, unlike the prior art, does not attempt to classify the impacted particles into several classifications, but simply into a first class which can beinhaled and a second class'which, if inhaled, would penetrate the lungs. This gives both a-simplified reading thereby requiring a minimum amount of time to check same while at the same time providing good class separation.

The apparatus of the invention includes generally a base which defines an upwardly opening chamber therein with a built-in critical size orifice which may be connected to a conventional vacuum source and a sealing member formed around the passage, a lower stage which fits onto the base in sealing engagement with the sealing member with frangible locking means to lock the lower stage onto the base in a sealed relationship therewith. A plurality of jet impaction passagesare provided through the lower stage to selectively impact particles in the gaseous medium onto a collection member which may be selectively positioned on the base within the chamber under the passages. An upper stage is carried on the lower stage and is provided with frangible locking means for selectively locking the upper stage onto the lower stage. A sealing ring is provided on the top of the lower stage which engages the upper stage in a sealing relationship therewith and the upper stage is provided with a plurality of larger diameters jet impaction passages for impacting larger particles in the gaseous medium passing therethrough onto a'collection member'supported by the lower stage. The jet impaction passages are sized to classify breathable particles in the upper stage and lung penetrating particles in the lower stage. The impaction passages are further provided with means for enhancing the flow characteristics through the passages to improve the performance thereof.

These and other features and advantages of the invention disclosed herein will become more apparent upon consideration of the following detailed description and accompanying drawings wherein like characters of reference designate corresponding parts throughout the several views and in which:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top plan view of one embodiment of the invention;

FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1;

FIG. 3 is an enlarged partial cross-sectional view taken along line 33 in FIG. 1 and showing the base and lower stage in partially exploded position;

FIG. 4 is an enlarged partial cross-sectional view taken substantially along line 4-4 in FIG. 1 and showing the upper and lower stages in partially exploded position;

FIG. 5 is a view similar to FIG. 3 showing the lower stage locked onto the base;

FIG. 6 is a view similar to FIG. 4 showing the upper stage locked onto the lower stage;

FIG. 7 is an enlarged partial cross-sectional view of the invention taken substantially along line 33 in FIG. 1 showing the device assembled;

FIG. 8 is an enlarged partial cross-sectional view of the device taken along substantially line 4-4 in FIG. 1 showing the device assembled;

FIG. 9 is an enlarged outside face view of one of the locking means on the lower stage of the invention;

FIG. 10 is an enlarged inside face view of one of the locking means on the lower stage of the invention;

FIG. 1 l is an enlarged outside face view of one of the locking means on the upper stage of the invention;

FIG. 12 is an inside face view of one of the locking means on the upper stage of the invention;

FIG. 13 is an enlarged partial cross-sectional view of the lower stage taken along line 13 13 in FIG. 1; and

FIG. 14 is an enlarged partial cross-sectional view taken along line 14-14 in FIG. 1 of the upper stage.

These figures and the following detailed description disclose specific embodiments of the invention, however, it is understood that the inventive concept is not limited thereto since it may be embodied in other forms.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Referring to the 'figures, it will be seen that the air sampling device 10 comprises generally a base 11, a lower stage 12 mounted on the base 11, and an upper stage 14 mounted on the lower stage 12. An upper collection member 15 as best seen in FIG. 2 is carried by the lower stage 12 for having the air-borne particles from the gaseous medium being sampled impinged thereon by the upper stage and a lower collection member 16 is carried by the base 11 to have the air-borne particles in the gaseous medium passing through the lower stage 12 impinged thereupon. The gaseous medium which is to be sampled is drawn through the upper stage 14 against the upper collection member 15, then around the collection member 15 and through the lower stage 12 against the lower collection member 16, and subsequently around the lower collection member 16 and out of the base 11.

The base 11 as best seen in FIGS. 2, 3, 5, 7 and 8 includes generally a circular web 20 from which depends an annular support flange 21 which has appropriate cut outs 22 formed therein to define support legs 24 on the flange 21 to support the base 11 in an upright position on an appropriate surface. The circular web 20 includes aa slightly conical central portion 25 in the center of which is provided an orifice 26. The orifice 26 has an outwardly flared approach section 28 which is connected on its downstream end to a generally cylindrical section 29. A hollow coupling tube 30 is provided concentrically about the orifice 26 and depends from the lower side of the conical central portion 25 for selective connection to appropriate vacuum source VS to draw a vacuum therethrough. An adaptor 31 may be provided for fitting on the coupling tube 30 which in turn is connected to a piece of flexible tubing T that is in turn connected to vacuum source VS schematically seen in FIG. 2.

An upstanding endless sealing flange 35 as best seen in FIG. 3 is provided adjacent the outside upper edge of the circular web 20 which has a generally vertical outer sealing face 36, an inner face 38 and an upper edge 39 which lies in a plane generally normal to the centerline CL of device 10 and concentrically thereabout. The sealing flange 35 has a height h to contact the lower stage 12 as will become more apparent. The outer circular edge of the circular web 20 is provided with an endless locking lip 40 which projects outwardly from the base of the sealing flange 35. The locking lip 40 defines an inwardly tapering upper guide surface 41 and a lower generally horizontal locking surface 42 which intersects the upper guide surface 41 to form a relatively sharp edge 44 as best seen in FIG. 3. The locking lip 40 is designed to engage and lock the lower stage 12 onto the base 11 as will be more fully explained.

Circumferentially spaced about the upper surface of the circular web 20 are a plurality of upstanding locators 45 which support and locate the lower collection member 16 thereon. Each of the locators 45 defines an inside upwardly facing, radially extending support surface 46 and an upstanding positioning tab 48 at the outer end of each of the support surfaces 46. The inside edges 49 of the upstanding positioning tabs 48 are located along a circle concentric with about the centerline CL of the device 10 and base 11 with a diameter d so that the collection member 16 will be supported by the surfaces 46 and located by the inside edges 49 of the tabs 48. It will be further noted that the inside supporting surfaces of the locators 45 lie in a common plane generally normal to centerline CL as will become more apparent.

The collection members 15 and 16 illustrated are for use primarily to collect viable samples, however, it is to be understood that alternate collection members may be substituted for. members 15 and 16 when collecting non-viable samples. The members 15 and 16 are both standard petri dishes 50 as best seen in FIGS. 2 and 7 which have an outside diameter substantially equal to the diameter d of the circle defined by the inside edges 49 of tabs 48. Each of the petri dishes 50 has an upstanding annular side wall 51 with a height h as will become more apparent. An agar layer 52 is provided in petri dishes 50 that have a nutrient material mixed therein to incubate viable organisms on the nutrient mixture. The layer 52 has an upper impaction surface 54 onto which the jet impaction passages impinge the gaseous medium as will become more apparent. The dishes 50 are filled with layer 52 to a standard height so that surface 54 is located a prescribed distance h:, from the bottom surface of dishes 50 as will be more fully explained. Thus, when collection member 16 is placed on locators 45, it is centered about centerline CL and supported so that the impaction surface 54 has a known location generally normal to centerline CL.

The lower stage 12 is adapted to fit on the base 11 so as to overlie the collection member 16. Stage 12 as seen in FIG. 2 includes a central circular aperture plate joined to an annular inverted U-shaped flange 61 around its periphery. The annular inside leg 62 of flange 61 is integral along its lower edge with the peripheral edge of plate 60 and extends upwardly therefrom with a prescribed obtuse angle A defined between leg 62 and plate 60 so that leg 62 flares outwardly about plate 60. The flange 61 as best seen in FIGS. 3 and 5 has an annular central web 64 oriented generally parallel to plate 60 and integral with the upper end of inside leg 62 along the inside edge of web 64. An annular outside positioning leg 65 of flange 61 is integral ,with the outside edge of central web 64 and depends therebelow defining an obtuse angle A with web 64.

The inside leg 62 as seen in FIG. 7 has a length l while the outside leg 65 has a longer length l as seen in FIG. 4 so that the lower edge 63 of leg 65 lies below the plane of leg 62 as will become more apparent.

The outside leg 65 has a first thickness t at its upper portion seen in FIG. 4 to define an upper annular section 66 and a second thickness t therebelow thinner than section 66 to define a frangible section 68. An upwardly facing reinforcing lip 69 is provided around the lower extending edge of the section 68 as will be more fully explained.

Circumferentially spaced about the lower edge of section 68 are a plurality of locking assemblies 70 seen in FIGS. 1, 3, 5, 7, 9 and which selectively lock the lower stage 12 onto the base 11. Each of the locking assemblies 70 includes a manually engagable breakoff tab 71 with a prescribed thickness t, adapted to be manually engaged as hereinafter explained to remove the lower stage 12 from the base 11. Each of the breakoff tabs 71 is located in the plane of the reinforcing lips 69 normal to centerline CL. A cutout 72 as seen in FIG. 9 is provided in the reinforcing lip 69 on opposite sides of the breakoff tab 71 to reduce the strength thereof as will become more apparent. Each of the breakoff tabs 71 is joined to the frangible section 68 of the leg 65 at its inside end and a pair of reinforcing ribs 74 seen in FIGS. 3, 5, 7 and 9 integral with both the breakoff tabs 71 and the frangible section 68 further connect the tab 71 to the frangible section 68. An inverted V-shaped cutout 75 is provided through the frangible section 68 centrally of the tab 71 with its bottom edge terminating in the plane of the upper surface of the tab 71. Directly behind the V-shaped cutout 75 at its lower end is an inwardly projecting locking tab 76 seen in FIGS. 3, 5, 7 and 10 which defines a locking surface 78 on the upper end thereof lying generally in the plane of the surface of the tab 71 and a downwardly and outwardly tapered guide surface 79 that extends from the inside corner 80 of the upper locking surface 78 to terminate at the inside surface of the lower edge of the frangible section 68. Spaced a prescribed distance d seen in FIG. 10 above the locking surface 78 of locking tab 76 is a positioning tab 81 generally aligned with the locking tab 76. The positioning tab 81 defines a bottom abutment surface 82 which faces the upper locking surface 78 of locking tab 76 and is generally parallel thereto. The abutment surface 82 is spaced above the upper locking surface 78 of locking tab 76 the prescribed distance d An upwardly and outwardly tapered surface 84 joins the inside corner 85 of abutment surface 82 with the inside of the frangible section 68 of leg 65. The inside diameter d of the frangible section 68 immediately above the upper locking surface 78 of locking tab 76 is substantially equal to the outside diameter of the'sharp edge 44 of locking lip 40 as will become more apparent.

Thus, it will be seen that as the lower stage 12 is placed over the upstanding sealing flange 35 of the base 11 and pushed toward the base 11, the tapered inside guide surfaces 79 of the locking tabs 76 will deflect the locking tabs 76 outwardly to enlarge the diameter of the frangible sction 68 sufficiently to allow the locking tab 76 to pass over the sharp edge 44 on the locking lip 40. Once the locking tab 76 passes over the locking lip 40, the resiliency of the frangible section 68 of leg 65 causes the locking tab 76 to snap back into position under the locking lip 40 so that the upper locking surfaces 78 of the locking tab 76 pass immediately under the lower locking surface 42 of the locking lip 40 as seen in FIG. 5. At the same time, the abutment surfaces 82 of the positioning tabs 81 engage the upper edge 63 of the sealing flange 35 so that the lower stage 12 is positively locked into position by the positioning tabs 81 and the locking tabs 76 engaging the sealing flange 35 and the locking lip 40. Because the distance d is substantially equal to the distance between the lower locking surface 42 of the locking lip 40 and the upper edge of the sealing flange 35, it will be seen that the stage 12 is positively positioned. While the frangible section 68 of leg 65 is sufficiently resilient to allow the tapered guide surfaces 79 on locking tab 76 to deflect the section 68 sufficiently outwardly to pass over the locking lip 40 on base 11, the upper locking surface 78 on the locking tab 76 in conjunction with the lower locking surface 42 on the locking lip 40 prevents the disassembly of the lower stage 12 from the base 11 without fracturing the frangible section 68 of the leg 65. When it is desirable to remove the lower section 12 from the base 1 1, the breakoff tabs 71 are manually engaged and the outer ends thereof are pivoted upwardly toward the leg 65 to cause the leg 65 to fracture from its lower edge beginning at the cutouts 72 in the reinforcing lip 69 on opposite sides of the tab 71 and extending upwardly substantially to the top edge of the frangible section 68 directly above the breakoff tab 71. The reinforcing ribs 74 ensure that this portion of the frangible section 68 of the leg 65 as seen by dashed lines in FIG. 9 will be fractured with the breakoff tab 71. This causes both the locking tab 76 and the positioning tab 81 to be removed with the breakoff tab 71. After each of these breakoff tabs 71 have been manually manipulated to break out that portion of the frangible section 68 of leg 65 associated therewith, it will be noted that the locking tabs 76 and positioning tabs 81 are no longer present in the frangible section 68 thereby precluding relocation of the lower stage 12 onto the base 11 so that adequate sampling is encountered. This ensures that the device then will not be re used in a contaminated state.

It will further be noted that when the locking tabs 76 snap under the locking lip 40 on base 11, the outer sealing face 36 of the sealing flange 35 on base 11 engages the inside surface of the frangible sections 68 to seal the same as seen in FIG. 5. This is because the inside surface of the frangible section 68 flares outwardly while the sealing face 36 of flange 35 extends generally vertically. Thus, a positive seal is formed between the base 11 and the lower stage 12. This forms a sealed chamber 86 best seen in FIG. 2 between the base 11 and the lower stage 12 with a space s seen in FIG. 7 around the side wall 51 of the dish 50 to allow the gaseous medium to pass from the impaction surface 54 of the member 16 over the side wall 51 thereof and then outwardly around the dish 50 and under the dish 50 between the locators 45 so that the vacuum source drawn on the chamber 86 through the orifice 26 will cause the gaseous medium to pass from the chamber 86.

The central plate 60 defines a plurality of jet impaction passages 90 seen in FIGS. 1, 7, and 13 therethrough arranged along radially extending paths P,with respect to'plate 60 and also along concentric circular paths P with respect to plate 60. Each of the jet impaction passages 90'defines a countersunk approach section 91 seen in FIG. 13 that opens onto the upper surface 92 of plate 60 at its large end and a cylindrical substantially constant diameter jet section 94 which extends from the lower end of the countersunk approach section 91 to the bottom surface 95 of plate 60. The countersunk approach section 91 serves to reduce the turbulence and enhance the laminar flow through the jet section 94 of the passages 90 to obtain better impacting characteristics of the air-borne particles in the gaseous medium passing therethrough. While the diameters of the jet sections 94 of the passages 90 may be varied to suit the particular circumstances, the diameter d illustrated is 0.01 66 inch. The thickness t of the plate 60 is 0.040 inch while the length 1 of the jet section 94 is 0.020 inch. The particular countersunk approach section 91 is a 60 countersink. The space s between the bottom surface 95 of the plate 60 and the impaction surface 54 on the collection member 16 is 0.05. inch. The arrangement of the locators 45, the locking lip 40, the locking tabs 76, the abutment surfaces 82, and the plate 60 are such to ensure this spacing will be produced when a standard petri dish 50 is placed on the locators 45 and is prefilled with the agar layer to a standard height. It will further be noted that there are 200 of the passages 90 illustrated in plate 60. A plurality of radially extending reinforcing ribs 96 bisect the space between radial paths P, of the passages 90 on the upper surface 92 of the plate 60 to both reinforce plate 60 and serve as a flow dividing mechanism to separate the flow of the gaseous medium passing to the passages 90 and the plate 60.

An annular upstanding sealing flange 100 seen in FIGS. 3-6 is located on the upper surface of the central web 64 of flange 61 and projects upwardly therefrom. The sealing flange 100 serves to provide a sealing relationship between the upper stage 14 and the lower stage 12 similarly to the sealing flange 35 between the base 11 and lower stage 12. The sealing flange 100 includes a generally vertical outside sealing face 101 with a diameter d and an inside face 102. The sealing flange 100 has a height h as will become more apparent. Thus, it will be seen that the upper surface of the central web 64 of flange 61 defines an upwardly facing abutting shoulder 104 to position the upper stage 14 as will become more apparent.

Also provided on the central web 64 of flange 61 inside the sealing flange 100 are a plurality of circumferentially spaced, radially extending locators 105 seen in FIGS. 4 and 6-8 similarly to locators 45 which define an inside upwardly facing, support surface 106 and an upstanding positioning tab 108 at the outer end of the inside support surface 106 so that the inside edges 109 of the positioning tabs 108 define a circle with a diameter d so that the petri dish 50 of collection member 15 will be supported and positioned thereby as will become more apparent.

Also provided along the lower surface of the central web 64 of the flange 61 are a plurality of circumferentially spaced, depending hold down flanges 100 seen in FIGS. 7 and 8 which extend generally radially with respect to the centerline CL of the device 10 and which have a prescribed depth d,. The spacing between the locators 45 and the bottom abutting edge 111 of tabs 110 is such that the edges 111 will engage the upper edge of the side wall 51 of the collection member 16 to maintain it in position when the lower stage 12 is locked onto the base 11.

The upper stage 14 seen in FIGS. 1 and 2 comprises generally a central circular plate 120 with an annular inverted generally U-shaped flange 121 integral with the outer periphery of plate 120. The flange 121 seen in FIGS. 6-8 includes an inside annular upstanding, leg 122 which is joined to the outer peripheral edge of the plate at its lower end and extends upwardly therefrom at an angle A with respect to plate 120. An annular central web 124 with an arcuate cross-section is joined to the upper edge of the inside leg 22 and an annular stepped outside leg 125 is joined with the outside edge of central web 124 and depends therebelow. The outside leg 125 is outwardly flaring and defines an angle A with the vertical. It will be further noted that the outside leg 125 has an outwardly stepped portion 126 intermediate its depth to define an annular downwardly facing abutment shoulder 128 seen in FIGS. 4 and 6 adapted to engage the upwardly facing abutting shoulder 104 of the lower stage 12 as will become more apparent. Thus, it will be seen that the outside leg 125 has an upper outwardly tapering portion 129 above the stepped portion 126 and a lower outwardly tapering portion 130 seen in FIG. 7 below the outwardly stepped portion 126. The lower edge of the lower portion 130 defines an outwardly facing reinforcing lip 131 therearound also seen in FIG. 7 which is generally located in a plane parallel to the plane of the circular plate 120. It will further be noted that the outside leg 125 has a thickness L, along its length.

Circumferentially spaced about the lower edge of the lower portion 130 of leg 125 are a plurality of locking assemblies 135 seen in FIGS. 1, 2, 4, 6, 8, 11 and 12. Each of the locking assemblies 135 includes a breakoff tab 136 which projects outwardly from the lower edge of the leg 125 generally horizontally. It will further be noted that each of the breakoff tabs 136 is connected to the lower edgeof the outside leg 125 through a frangible section 138 best seen in FIGS. 4 and 11. The frangible section 138 is generally rectilinear in shape with a thickness approximately equal to the thickness at its upper end and tapered so that it is substantially thinner at its lower end with a thickness t It will also be seen that the frangible section 138 interrupts the reinforcing lip 131 seen in FIG. 11 to reduce the strength. of the frangible section 138 below the strength of the lower portion 130 of leg 125 as will become more apparent. The frangible section 138 projects below the reinforcing lip 131 a prescribed distance d and mounts the breakoff tab 136 at the lower end thereof. A pair of upstanding reinforcing ribs 139 connect the upper surface of the breakoff tab 136 with the frangible section 138 to ensure that the frangible section 138 will be frac v tured as the breakoff tab is lifted as will become more apparent. An inverted V-shaped cutout 140 is provided through the frangible section 138 immediately above the breakoff tab 136 which terminates at the plane, of the upper surface of the breakoff tab 136. A locking tab 141 seen in FIGS. 6 and 12 is provided on the inside of the frangible section 138 immediately behind the breakoff tab 136 which defines an upper locking surface 142 lying generally in the plane of the upper surface of the breakoff tab 136. A guide surface 144 extends from the inside corner 145 of surface 142 downwardly and outwardly to the lower edge of the frangible section 138. The upper locking surface 142 is spaced below the downwardly facing abutment shoulder 128 in outside leg 125 a prescribed distance d, seen in FIG. 6 which corresponds to the distance between the upwardly facing abutting shoulder 104 on the lower stage 12 and the bottom of the reinforcing lip 69 along the lower edge of the outside leg 65 of the lower stage 12. Thus, it will be seen that when the upper stage 14 is positioned over the lower stage 12 so that is is substantially concentric with respect to the centerline CL of the device 10, it can be forced downwardly onto the lower stage 12 whereupon the guide surfaces 144 on the locking tab 141 deflect the frangible sections 138 sufficiently far outwardly to allow the locking tabs 141 to pass over the reinforcing lip 69 on the lower section 12. When the downwardly facing abutment shoulder 128 on the upper section 14 engages the upwardly facing abutment shoulder 104 on the lower stage 12, the locking tabs 141 pass around the reinforcing lip 69 on stage 12 to allow the upper locking surfaces 144 to pass under the lower edge of the reinforcing lip 69. Thus, it will be seen that the upper stage 14 is positively located with respect to the lower stage 12 by the locking tabs 141 and the abutment shoulder 128. While the material of the upper stage 14 is sufficiently resilient to allow the guide surfaces 144 to deflect the locking tab 144 outwardly, the resiliency thereof is not sufficient to allow the upper stage 14 to be removed from the lower stage 12 without fracturing the frangible section 138. When it is desirable to remove the upper stage 14 from the lower stage 12, the breakoff tabs 136 are manually engaged and the tab 136 pivoted upwardly toward the outside leg 125 of flange 121 so that the frangible sections 138 fracture as indicated by dashed lines FIG. 1 1 and the breakoff tabs 136 and the fractured portions of the frangible sections 138 are removed from the outside leg 125. It will also be noted that the reinforcing rib 139 ensures that the locking tabs 141 will be fractured from the frangible section 138 as and incidence to the release of the upper stage 14 of the lower stage 12. This ensures that the upper stage 14 will not be reused in a contaminated condition.

It will further be noted that the inside outwardly flaring surface of the upper portion 129 of outside leg 125 will engage the sealing flange 100 on top of the lower stage 12 to cause the outside sealing face 101 thereof to engage the inside surface of the upper portion 129 to seal the upper stage 14 to the lower stage 12. Thus, it will be seen that a sealed chamber 146 best seen in FIG. 2 will be defined between the lower stage 12 and the upper stage 14. It will further be seen that a space s best seen in FIG. 7 will be defined around the side wall 51 of the upper collection member so that the gaseous medium passing onto the upper collection member 15 can pass around the side wall 51 thereof and around the outside of the sidewall 51 back under the collection member 15 above the upper surface 92 of the plate 60 of lower stage 12.

It will further be noted that a plurality of hold down tabs 148 seen in FIGS. 7 and 8 are circumferentially spaced about the underside of the central web 124 of flange 121 which extend generally radially with respect to the centerline CL and define a bottom abutting edge 149 thereon which engage the upper edge of the side wall 51 of the upper collection member 15 to positively hold it in position.

The central circular plate 120 defines a plurality of jet impaction passages 150 therethrough spaced along generally radially extending paths P and along concentric paths P about the centerline CL as seen in FIG. 1. It will further be noted that eachof the jet impaction passages 150 as seen in FIG. l4 have a countersunk approach section 151 with the larger dimension thereof opening onto the upper surface 152 of'the plate 120. A constant diameter cylindrical jet section 154 extends downwardly from the countersunk approach section 151 and opens onto the bottom surface 155 of plate 120. The countersunk approach sections 151 serve generally the same purposes as the sections 91 for the passages and the operation thereof is generally the same. It will be noted, however, that the diameter d of the jet section 154 is larger than the diameter d of the corresponding section 94 of passages 90 as will be more fully explained. It will further be noted that the plate has a thickness t and the jet section 154 has a length While the diameter d may be varied to meet the particular requirements, a diameter d of 0.0585 inch and the length of the jet section 154 is 0.060 inch. The space S;; between the bottom surface 155 of plate 120 and the impaction surface 54 of the collection member 15 is illustrated as 0.125 inch. It will further be noted that there are 200 passages in the plate 120. The passages 150 seen in FIG. 1 along the inside concentric circular path P have a constant diameter jet section with a length of 0.080 inch.

It will further be noted that the bottom surface of plate 120 has a plurality of sector shaped recesses 156 formed therein bisecting the space between the radial paths P, as seen by dashed lines in FIG. 1 to form a depending ridge 158 best seen in FIG. 14 therebetween through which the passages 150 extend. It will be noted that the side walls 159 of the depending ridge 158 both flare outwardly and upwardly and that the outer end wall 160 of the recess 156 extends inwardly and upwardly from the bottom surface 155 of plate 120. Thus, as the gaseous medium is injected through the passages 150 onto the impaction surface 54, of collection member 15, the recesses 156 provide an additional space for the impaction jets of the gaseous medium to expand therein as illustrated in FIG. 14 and to be directed radially outward towards the side wall 51 of the collection member 15 to pass therearound and down into the lower stage 12. It will be noted that the configuration of the locking tabs 141, downwardly facing abutment 128 and the plate 120 are configured so that the bottom surface 155 of the plate 120 is always located the distance s;; from the impaction surface 54 of the collection member 15 to obtain proper particle classification.

The base 11, lower stage 12 and upper stage 14 are manufactured of a material which exhibits the fracturable characteristics outlined above. While any number of materials may be used, one such material that has been used satisfactorily is a high impact polystyrene plastic that lends itself to low cost, high production injection molding techniques to reduce the manufacturing cost thereof.

The diameter of the cylindrical section 29 of orifice 26 is selected to provide a prescribed flow rate through the device 10 over a wide range of vacuum. Thus, the diameter of the section 29 is a critical diameter orifice so that sonic velocity is reached by the gaseous medium being drawn therethrough when a minimum vacuum is imposed thereon. For the particular size device 10 illustrated, the diameter of section 29 is 0.0733 inch to produce a 1 cubic foot/minute flow rate through the device when any vacuum above 9 inches Hg. is imposed thereon. Because the orifice 26 is made an integral part of the base 11, better flow control of the gaseous medium is produced.

' Assuming 1 cubic foot per minute of gaseous medium such as air is passing through the device 10, the upper stage '14 using the dimensions described hereinabove I has an efficiency cut off diameter of 7.0 microns. The

lower stage 12, using a l cubic foot per minute flow rate and the dimensions set forth heretofore has an efficiency cut off diameter of 1.05 microns. Thus, the upper stage 14 indicates inhalable particles while the lower stage 12 indicates particles that can penetrate the lungs.

If it is desirable to sample non-viable particles, then petri dishes 50 would be replaced by members which have a thickness corresponding to the dish 50 and layer 52 so that an impaction surface would be provided corresponding to surface 54. To hold the non-viable collection members in place, an appropriate flange would be provided to engage the hold down tabs 110 or 148.

While specific embodiments of the invention have been disclosed herein, it is to be understood that full use may' be made of modifications, substitutions and equivalents without departing from the scope of the inventive concept.

I claim:

1. A disposable multi-stage sampling device for separating particles from a gaseous medium by jet impaction comprising: i

a plurality of stages serially connected to define a sealed passage between said stages for the passage of the gaseous medium between stages, each of said stages defining a plurality ofjet impaction passages therein through which the gaseous medium passes, each of said stages including a collection member operatively associated with said jet impaction passages of said stage to cause certain size particles in the gaseous medium to be impacted onto said collection member as the gaseous medium passes through said jet impaction passages; and

frangible means operatively connecting said stages together, said frangible means constructed and arranged to be destroyed as an incident to the separation of said stages to prevent reassembly thereof, said frangible means including first locking means and second locking means adapted to engage each other to maintain said stages in a sealed relation with each other, said frangible means further including a frangible member connecting said first locking means to one of said stages so that said frangible member prevents disengagement of said first locking means from said second locking means without fracture of said frangible member to separate said first locking means from said one of said stages.

2. The sampling device of claim 1 wherein said first locking means includes at least one first abutment member and at least one first locking member, and wherein said second locking means includes at least one second abutment member and at least one second locking member, said first abutment member and said first locking member connected to said one of said stages by said frangible member, said first abutment member engaging said second abutment member when said first locking member engages said second locking member to positively position said stages with respect to each other.

3. The sampling device of claim 2 wherein said first abutment member and said first locking member are both removed from said one of said stages as said frangible member fractures as an incident to the separation of said stages.

4. A disposable multi-stage sampling device for separating particles from a gaseous medium by jet impaction comprising:

a plurality of stages serially connected to define a sealed passage between said stages for the passage of the gaseous medium between stages, each of said stages defining a plurality of jet impaction passages therein through which the gaseous medium passes, each of said stages including a collection member operatively associated with said jet impaction passages of said stage to cause certain size particles in the gaseous medium to be impacted onto said collection member as the gaseous medium passes through said jet impaction passages;

a base means carrying said stages; and,

frangible means operatively connecting said stages together, said frangible means constructed and arranged to be destroyed as an incident to the separation of said stages to prevent reassembly thereof, said frangible means including base locking means for operatively connecting said lowermost stage to said base means, and stage locking means operatively connecting each of said other stages to the next lower stage, both said base locking means and said stage locking means constructed and arranged to be destroyed as an incident to the separation of said stages and said base means.

5. A disposable multi-stage sampling device for separating particles from a gaseous medium by jet impaction comprising:

a base member having a centerline including a circular central web and an annular sealing flange extended upwardly from said central web adjacent the periphery thereof, and an annular locking lip about the periphery of said central web including an outwardly angled deflection surface and a lower locking surface generally normal to the centerline of said base, and a critical size orifice through said circular web centrally thereof through which a vacuum may be imposed;

a lower stage including a first circular apertured plate with a bottom surface, a first inverted U-shaped annular flange about the periphery of said apertured plate, said annular flange including a first outside depending annular leg adapted to fit around the periphery of said central web of said base, first locking means carried by said outside leg for selectively engaging said locking surface of said locking lip on said base member, first positioning means adapted to engage said sealing flange on said base for selectively positioning said lower stage and said bottom surface of said first apertured plate with respect to said circular web of said base member, and first frangible means operatively connecting said first locking means and said first positioning means with said outside leg so that said first locking means can resiliently pass over said locking lip but cannot be removed from said locking lip .without destruction of said first frangible means to remove said first locking means and said first positioning means from said outside leg, said first apertured plate defining a plurality of first jet impaction passages therethrough arranged normally parallel to the centerline of said base member; and

an upper stage including a second circular apertured plate, a .second inverted U-shaped flange around the periphery of said second apertured plate, said second flange including an outside second leg adapted to fit over said first outside leg of said lower stage, second locking means for selectively engaging said first outside leg of said lower stage member to lock said upper stage onto said lower stage, second frangible means connecting said second locking means with said second outside leg so that said second locking means can resiliently engage said lower stage member but said upper stage cannot be removed from said lower stage without destruction of said second frangible means to remove said second locking means from said second outside leg of said upper stage, and second positioning means for selectively positioning said second apertured plate with respect to said first apertured plate.

6. The disposable sampling device of claim 1 further including flow direction control means operatively associated with each of said stages for inducing generally radial flow of the gaseous medium with respect to said stages as the gaseous medium passes between stages.

7. The disposable sampling device of claim 1 wherein each of said jet impaction passages includes a flow forming section on the upstream end of said passage for generating a laminar flow through said passage and a jet impaction section connected to said fiow producing section downstream thereof for generating a jet impaction gaseous medium stream generally normal to said collection medium and of a prescribed velocity for a prescribed flow rate of gaseous medium therethrough.

8. The disposable sampler of claim 1 further including vacuum producing means; and flow control means operatively connecting said vacuum producing means with said sealed passage downstream of said stages. said flow control means defining a critical size orifice therein through which the gaseous medium passes to said vacuum producing means to cause a constant flow of the gaseous medium through the device when said vacuum producing means imposes a vacuum on said passage above a minimum prescribed value.

9. A disposable multi-section sampling device for separating particles from a gaseous medium by jet impaction comprising:

an impaction member defining a plurality of jet impaction passages therethrough through which the gaseous medium passes;

a collection member onto which the particles in the gaseous medium are to be impacted;

support means for positioning said collection memher with respect to said jet impaction passages so that said collection member is operatively associated with said passages to cause the particles in the gaseous medium to be impacted onto said collection member as the gaseous medium passes through said jet impaction passages; and

frangible means operatively connecting said impaction member and said support means together, said frangible means constructed and arranged to be destroyed as an incident to the separation of said impaction member and said support means to prevent reassembly thereof, and said frangible means including first locking means and second locking means adapted to engage each other to maintain said impaction member and said support means in a sealed relationship with each other, said first locking means being frangible so that disengagement of said first locking means from said second locking means fractures said first locking means to prevent re-engagement of said first locking means with said second locking means to reconnect said impaction member and said support means together.

10. A sampling device for separating entrained particles from a gaseous medium by jet impaction comprising:

an impaction member having a first centerline, said impaction member defining a plurality of jet impaction passages therethrough to direct the gaseous medium along spaced paths generally parallel to said first centerline, and said impaction member further including an annular depending resilient flange defining a first annular sealing surface thereon concentrically arranged about said first centerline; collection member onto which the particles in the gaseous medium are to be impacted;

a support member having a second centerline for positioning said collection member with respect to said jet impaction passages so that said collection member is operatively associated with said passage to cause the particles in the gaseous medium to be impacted onto said collection member as the gaseo'us medium passes through said jet impaction passages, said support member including an upstanding resilient flange defining a second annular sealing surface thereon concentrically arranged about said second centerline, said first and second sealing surfaces constructed and arranged to resiliently engage each other when said first centerline of said impaction member is coaxially arranged with said second centerline of said support member to define an operating chamber therein sealed by said first and second sealing surfaces; and,

connection means releasably connecting said impaction member and said support member to selectively maintain said first and second sealing surfaces in sealing engagement with each other.

11. A disposable multi-section sampling device for separating particles from a gaseous medium by jet impaction comprising:

a base member having a centerline including a circular central web and an annular sealing flange extended upwardly from said central web adjacent the periphery thereof, and an annular locking lip about the periphery of said central web including an outwardly angled deflection surface and a lower locking surface generally normal to the centerline of said base; and,

an impaction stage including a first circular aper tured plate with a bottom surface, a first inverted U-shaped annular flange about the periphery of said apertured plate, said annular flange including a first outside depending annular leg adapted to fit around the periphery of said central web of said base, first locking means carried by said outside leg for selectively engaging said locking surface of said locking lip on said base member, first positioning means adapted to engage said sealing flange on said base for selectively positioning said lower stage and said bottom surface of said first apertured plate with respect to said circular web of said base member, and first frangible means operatively connecting said first locking means and said first positioning means with said outside leg so that said first locking means can resiliently pass over said locking lip but cannot be removed from said locking lip without destruction of said first frangible means to remove said first locking means and said first positioning means from said outside leg, said first apertured plate defining a plurality of first jet impaction passages therethrough arranged normally parallel centerline and spaced above said first jet plate a to the centerline of said base member. third prescribed distance, and defining a second 12. A multi-stage sampling device for separating encollection surface thereon on that side opposite train d parti l s fr m a gas medium y j P said first jet plate oriented generally normal to said tion comprising: centerline;

a base member having a centerline and including a a second impaction stage including a second jet plate central web defining an outlet therethrough through which the gaseous medium passes, and base collection support means;

having an upper surface and a lower surface generally parallel to each other and oriented generally normal to said centerline, and an annular support a first collection member carried by said base support 10 section connected to Said Second jet plate and means concentr cally about said centerline and ported on Said first impaction Stage so that Said SPaced above sald (fentral first prescnbed lower surface of said second jet plate is supported dlstance and de,fmmg a first Pollectlon Surfac? a fourth prescribed distance above said second coliz g gg gr; sf iig lzs gg izmfig lection surface, said second stage sealed with rea first im action sta e includin a first 'et late hav- Spect to.sald first stage to definean annulz-lr space ing an Epper surfaie and a lo ver surf ace generally g fg i fig igifiz zzz mal to said centerline, and an annular support sect t l t d t lat d in a tion connected to said first jet plate and supported Je p a Sal Je e e m g p on said base member so that said lower surface of rahty of Jet lmpacnon pas.sages ther?- said first jet plate is supported a second prescribed through for f the gaseous medium onto Said distance above said first collection surface, said Second collectlon.surface l g a pa th generally first stage sealed with respect to said base member normal thereto Sald second lmpactwnPassages to define an annular space connecting the space ar ranged along geferany radially extendmg. paths between said first jet plate and said first collection wlth respec? to Sald F f f and further f member with the space between said first collec- "K 3 pluramy of flow refzesses defined m tion member and Said central web Said first jet sa d lower surface of said second et plate between plate defining a plurality of first jet impaction pasradlally extendlng P each of said flow Cli- Sages therethrough for directing the gaseous viding recesses extending generally radially with dium onto said first collection surface along a path respect to Said centerlme so that the gaseous generally normal thereto, said first jet impaction dium Passing first through Said Second l p passages arranged along generally radially extendtion Passages, and Subsequently through Said first ing paths with respect to said centerline and further l impaction Passages is evenly distributed circumi l di a l li f fl di idi ib projecting ferentially about said centerline by said flow dividupwardly from said upper surface of said first jet g recesses as Said gaseous medium Passes plate between said radially extending paths, each of ar ly in the Space between the second jet impacsaid flow dividing ribs extending generally radially n P te d a d Second Collection member and with respect to said centerline; said first stage furby said flow dividing ribs as said gaseous medium ther including first collection support means; passes inwardly in the space between the second a second collection member carried by said first colcollection member and the first jet plate.

lection support means concentrically about said 

1. A disposable multi-stage sampling device for separating particles from a gaseous medium by jet impaction comprising: a plurality of stages serially connected to define a sealed passage between said stages for the passage of the gaseous medium between stages, each of said stages defining a plurality of jet impaction passages therein through which the gaseous medium passes, each of said stages including a collection member operatively associated with said jet impaction passages of said stage to cause certain size particles in the gaseous medium to be impacted onto said collection member as the gaseous medium passes through said jet impaction passages; and frangible means operatively connecting said stages together, said frangible means constructed and arranged to be destroyed as an incident to the separation of said stages to prevent reassembly thereof, said frangible means including first locking means and second locking means adapted to engage each other to maintain said stages in a sealed relation with each other, said frangible means further including a frangible member connecting said first locking means to one of said stages so that said frangible member prevents disengagement of said first locking means from said second locking means without fracture of said frangible member to separate said first locking means from said one of said stages.
 2. The sampling device of claim 1 wherein said first locking means includes at least one first abutment member and at least one first locking member, and wherein said second locking means includes at least one second abutment member and at least one second locking member, said first abutment member and said first locking member coNnected to said one of said stages by said frangible member, said first abutment member engaging said second abutment member when said first locking member engages said second locking member to positively position said stages with respect to each other.
 3. The sampling device of claim 2 wherein said first abutment member and said first locking member are both removed from said one of said stages as said frangible member fractures as an incident to the separation of said stages.
 4. A disposable multi-stage sampling device for separating particles from a gaseous medium by jet impaction comprising: a plurality of stages serially connected to define a sealed passage between said stages for the passage of the gaseous medium between stages, each of said stages defining a plurality of jet impaction passages therein through which the gaseous medium passes, each of said stages including a collection member operatively associated with said jet impaction passages of said stage to cause certain size particles in the gaseous medium to be impacted onto said collection member as the gaseous medium passes through said jet impaction passages; a base means carrying said stages; and, frangible means operatively connecting said stages together, said frangible means constructed and arranged to be destroyed as an incident to the separation of said stages to prevent reassembly thereof, said frangible means including base locking means for operatively connecting said lowermost stage to said base means, and stage locking means operatively connecting each of said other stages to the next lower stage, both said base locking means and said stage locking means constructed and arranged to be destroyed as an incident to the separation of said stages and said base means.
 5. A disposable multi-stage sampling device for separating particles from a gaseous medium by jet impaction comprising: a base member having a centerline including a circular central web and an annular sealing flange extended upwardly from said central web adjacent the periphery thereof, and an annular locking lip about the periphery of said central web including an outwardly angled deflection surface and a lower locking surface generally normal to the centerline of said base, and a critical size orifice through said circular web centrally thereof through which a vacuum may be imposed; a lower stage including a first circular apertured plate with a bottom surface, a first inverted U-shaped annular flange about the periphery of said apertured plate, said annular flange including a first outside depending annular leg adapted to fit around the periphery of said central web of said base, first locking means carried by said outside leg for selectively engaging said locking surface of said locking lip on said base member, first positioning means adapted to engage said sealing flange on said base for selectively positioning said lower stage and said bottom surface of said first apertured plate with respect to said circular web of said base member, and first frangible means operatively connecting said first locking means and said first positioning means with said outside leg so that said first locking means can resiliently pass over said locking lip but cannot be removed from said locking lip without destruction of said first frangible means to remove said first locking means and said first positioning means from said outside leg, said first apertured plate defining a plurality of first jet impaction passages therethrough arranged normally parallel to the centerline of said base member; and an upper stage including a second circular apertured plate, a second inverted U-shaped flange around the periphery of said second apertured plate, said second flange including an outside second leg adapted to fit over said first outside leg of said lower stage, second locking means for selectively engaging said first outside leg of said lower stage member to lock said upper stage onto said lower stage, second frAngible means connecting said second locking means with said second outside leg so that said second locking means can resiliently engage said lower stage member but said upper stage cannot be removed from said lower stage without destruction of said second frangible means to remove said second locking means from said second outside leg of said upper stage, and second positioning means for selectively positioning said second apertured plate with respect to said first apertured plate.
 6. The disposable sampling device of claim 1 further including flow direction control means operatively associated with each of said stages for inducing generally radial flow of the gaseous medium with respect to said stages as the gaseous medium passes between stages.
 7. The disposable sampling device of claim 1 wherein each of said jet impaction passages includes a flow forming section on the upstream end of said passage for generating a laminar flow through said passage and a jet impaction section connected to said flow producing section downstream thereof for generating a jet impaction gaseous medium stream generally normal to said collection medium and of a prescribed velocity for a prescribed flow rate of gaseous medium therethrough.
 8. The disposable sampler of claim 1 further including vacuum producing means; and flow control means operatively connecting said vacuum producing means with said sealed passage downstream of said stages. said flow control means defining a critical size orifice therein through which the gaseous medium passes to said vacuum producing means to cause a constant flow of the gaseous medium through the device when said vacuum producing means imposes a vacuum on said passage above a minimum prescribed value.
 9. A disposable multi-section sampling device for separating particles from a gaseous medium by jet impaction comprising: an impaction member defining a plurality of jet impaction passages therethrough through which the gaseous medium passes; a collection member onto which the particles in the gaseous medium are to be impacted; support means for positioning said collection member with respect to said jet impaction passages so that said collection member is operatively associated with said passages to cause the particles in the gaseous medium to be impacted onto said collection member as the gaseous medium passes through said jet impaction passages; and frangible means operatively connecting said impaction member and said support means together, said frangible means constructed and arranged to be destroyed as an incident to the separation of said impaction member and said support means to prevent reassembly thereof, and said frangible means including first locking means and second locking means adapted to engage each other to maintain said impaction member and said support means in a sealed relationship with each other, said first locking means being frangible so that disengagement of said first locking means from said second locking means fractures said first locking means to prevent re-engagement of said first locking means with said second locking means to reconnect said impaction member and said support means together.
 10. A sampling device for separating entrained particles from a gaseous medium by jet impaction comprising: an impaction member having a first centerline, said impaction member defining a plurality of jet impaction passages therethrough to direct the gaseous medium along spaced paths generally parallel to said first centerline, and said impaction member further including an annular depending resilient flange defining a first annular sealing surface thereon concentrically arranged about said first centerline; a collection member onto which the particles in the gaseous medium are to be impacted; a support member having a second centerline for positioning said collection member with respect to said jet impaction passages so that said collection member is operatively associated with said passage to caUse the particles in the gaseous medium to be impacted onto said collection member as the gaseous medium passes through said jet impaction passages, said support member including an upstanding resilient flange defining a second annular sealing surface thereon concentrically arranged about said second centerline, said first and second sealing surfaces constructed and arranged to resiliently engage each other when said first centerline of said impaction member is coaxially arranged with said second centerline of said support member to define an operating chamber therein sealed by said first and second sealing surfaces; and, connection means releasably connecting said impaction member and said support member to selectively maintain said first and second sealing surfaces in sealing engagement with each other.
 11. A disposable multi-section sampling device for separating particles from a gaseous medium by jet impaction comprising: a base member having a centerline including a circular central web and an annular sealing flange extended upwardly from said central web adjacent the periphery thereof, and an annular locking lip about the periphery of said central web including an outwardly angled deflection surface and a lower locking surface generally normal to the centerline of said base; and, an impaction stage including a first circular apertured plate with a bottom surface, a first inverted U-shaped annular flange about the periphery of said apertured plate, said annular flange including a first outside depending annular leg adapted to fit around the periphery of said central web of said base, first locking means carried by said outside leg for selectively engaging said locking surface of said locking lip on said base member, first positioning means adapted to engage said sealing flange on said base for selectively positioning said lower stage and said bottom surface of said first apertured plate with respect to said circular web of said base member, and first frangible means operatively connecting said first locking means and said first positioning means with said outside leg so that said first locking means can resiliently pass over said locking lip but cannot be removed from said locking lip without destruction of said first frangible means to remove said first locking means and said first positioning means from said outside leg, said first apertured plate defining a plurality of first jet impaction passages therethrough arranged normally parallel to the centerline of said base member.
 12. A multi-stage sampling device for separating entrained particles from aa gaseous medium by jet impaction comprising: a base member having a centerline and including a central web defining an outlet therethrough through which the gaseous medium passes, and base collection support means; a first collection member carried by said base support means concentrically about said centerline and spaced above said central web a first prescribed distance, and defining a first collection surface thereon on that side opposite said central web oriented generally normal to said centerline; a first impaction stage including a first jet plate having an upper surface and a lower surface generally parallel to each other and oriented generally normal to said centerline, and an annular support section connected to said first jet plate and supported on said base member so that said lower surface of said first jet plate is supported a second prescribed distance above said first collection surface, said first stage sealed with respect to said base member to define an annular space connecting the space between said first jet plate and said first collection member with the space between said first collection member and said central web, said first jet plate defining a plurality of first jet impaction passages therethrough for directing the gaseous medium onto said first collection surface along a path generally normal thereto, said first jet impaction passages arranged along generAlly radially extending paths with respect to said centerline and further including a plurality of flow dividing ribs projecting upwardly from said upper surface of said first jet plate between said radially extending paths, each of said flow dividing ribs extending generally radially with respect to said centerline; said first stage further including first collection support means; a second collection member carried by said first collection support means concentrically about said centerline and spaced above said first jet plate a third prescribed distance, and defining a second collection surface thereon on that side opposite said first jet plate oriented generally normal to said centerline; a second impaction stage including a second jet plate having an upper surface and a lower surface generally parallel to each other and oriented generally normal to said centerline, and an annular support section connected to said second jet plate and supported on said first impaction stage so that said lower surface of said second jet plate is supported a fourth prescribed distance above said second collection surface, said second stage sealed with respect to said first stage to define an annular space connecting the space between said second jet plate and said second collection member with the space between said second collection member and said first jet plate, said second jet plate defining a plurality of second jet impaction passages therethrough for directing the gaseous medium onto said second collection surface along a path generally normal thereto, said second jet impaction passages arranged along generally radially extending paths with respect to said centerline and further including a plurality of flow dividing recesses defined in said lower surface of said second jet plate between said radially extending paths, each of said flow dividing recesses extending generally radially with respect to said centerline so that the gaseous medium passing first through said second jet impaction passages and subsequently through said first jet impaction passages is evenly distributed circumferentially about said centerline by said flow dividing recesses as said gaseous medium passes outwardly in the space between the second jet impaction plate and said second collection member and by said flow dividing ribs as said gaseous medium passes inwardly in the space between the second collection member and the first jet plate. 